Voltage transformer 230 to 115V

Discussion in 'The Projects Forum' started by sunnyswh, Dec 19, 2014.

  1. sunnyswh

    Thread Starter New Member

    Dec 19, 2014
    12
    0
    I have collected a voltage transformer and a fan from a SCHOTT light source. I guess they are good parts. Just bought and audio system from US and wondering if I can use these parts to make a voltage transformer myself to use the 110v audio system in Singapore where 230V is used.

    I am not experienced with electrics, but I guess since the parts are almost ready to use, I should be able to do it.

    I have a pictures attached.

    questions:

    1. I think the transformer is able to convert from 230v to 115v if I am correct about the label. Am I right?

    2. It is an old part and I have been trying to find design/wiring plan of the product but not successful. I think the three wire already there is the input and the other side is the output. which two shall I connect to get 115V? can I plug the 230V side and use a multimeter to test what combination to give me 115V?

    3. the audio system is 60W, and the transformer and bear 150W (am I right?). Do I need a fan since I will need the transformer on all the time to play the audio?

    4. Do I need control circuit or this simple transformer do work for the audio system?

    5. what other practical cautions?

    Thanks you very much for any advices!

    IMAG0190.jpg IMAG0189.jpg
     
  2. MikeML

    AAC Fanatic!

    Oct 2, 2009
    5,450
    1,066
    This tranny is not really designed for your application, but it appears to have a center-tap on the 230V primary winding, so you might be able to use it as an autotransformer. It should be good for your 60W stereo without a fan. However, you will need a Multimeter to determine how to hook it up. Do you have one?


    It should be mounted in an fireproof enclosure. You will need a line cord with plug, a grommet,

    an on-off toggle switch rated at 230V 5A,

    a fuse-holder and fuse,

    and a US style duplex outlet.
     
    Last edited: Dec 19, 2014
  3. sunnyswh

    Thread Starter New Member

    Dec 19, 2014
    12
    0
    Thanks a lot MikeML! I will give it a go. Unfortunately, I cut it out of the light source box and threw the rest since I did not what to do with it at the time. I do not even remember how the input side it connected. I wish it will be neutral, earth and live from the left to the right. How can I test if I am right or not? For the fuse, since Singapore uses the UK plug, can I just use a UK plug with fuse fixed in without using another fuse in the enclosure with the transformer?
     
  4. ScottWang

    Moderator

    Aug 23, 2012
    4,857
    767
  5. MikeML

    AAC Fanatic!

    Oct 2, 2009
    5,450
    1,066
    No. Do not attempt to wire it without confirming the measurements I will have you do. You never answered if you have a multimeter.

    Yes, but if you dont put a switch in the primary, the transformer will always be on (even if the stereo is off) and be wasting substantial power.
     
  6. sunnyswh

    Thread Starter New Member

    Dec 19, 2014
    12
    0
     
  7. MikeML

    AAC Fanatic!

    Oct 2, 2009
    5,450
    1,066
    Look at three terminals on the transformer primary. They are the ones without the cut off wires (on the bottom of your picture). Lets call them A, B, and C, from left to right. We need to identify which is the Center-Tap (ct). Using your Multimeter in its LOW Ω mode, measure the DC resistance from A-B, B-C, and A-C. Post your results.
     
  8. MaxHeadRoom

    Expert

    Jul 18, 2013
    10,571
    2,381
    By the apparent number of turns and the gauge of wire on the secondary, it appears they are the low voltage mentioned on the side, 15v/13v.
    If one of the terminals on the primary (bottom side) has two wires attached, this will be the C.T. if it has one.
    Max.
     
  9. sunnyswh

    Thread Starter New Member

    Dec 19, 2014
    12
    0
    Hi Mike, here are the results: A-B (0.3Ω), B-C (0.3Ω), A-C (0.4Ω)

    I also measured the bottom terminals, let's call them x, y, and z from the left to the right

    x-y (4.7Ω), y-z (5.4Ω), x-z (9.9Ω)
     
  10. sunnyswh

    Thread Starter New Member

    Dec 19, 2014
    12
    0
    Hi Max, I can see the middle terminal (B, as we named it in Mike's post) on the primary side has two wires and the middle one (y) on the secondary side has two wires.

    the side of the transformer looks like: Sek. 15V10A/13V9.2A-115V p. I thought it could transfer 230 to 115V since the fan it was powering was on 115V (as attached) IMAG0196.jpg
     
  11. MikeML

    AAC Fanatic!

    Oct 2, 2009
    5,450
    1,066
    I asked you to measure the "bottom terminals", as I thought they are the primary windings. The ones with the cut-off wires are the secondary, which you will not be using. Your measurements confirm that.

    Connect your neutral to x. Connect your fused 230V line to z. Take your 115V output between x and y. If you have a US duplex outlet, connect x (neutral) to the silver screw on the outlet. Connect y to the bronze screw. Connect the earth wire from your British line cord through to the Green screw on the outlet.

    Plug in the input cord with nothing connected on the duplex outlet side, and using your Multimeter on its AC setting, measure the voltage between the bronze and silver screw (or between x and y). It should read close to half the input voltage.

    Just to be clear:
    tran.jpg
     
    Last edited: Dec 20, 2014
  12. sunnyswh

    Thread Starter New Member

    Dec 19, 2014
    12
    0
    Thanks Mike! Sorry I made a mistake with which side you referred. So according to your last post, I just need one side and that is enough. Was not expecting it could be so simple.

    Since the light source was used in our lab where we used 240V in UK and 230V in Singapore, I guess the wiring should transfer 230/240V to 115V just as I need and the fan needs. Then what are the cut off wires for? what would I get from those wires? Can I connect the terminals as you suggested and measure them without anything connected?
     
  13. sunnyswh

    Thread Starter New Member

    Dec 19, 2014
    12
    0
    thanks! it is very clear with your picture
     
  14. MikeML

    AAC Fanatic!

    Oct 2, 2009
    5,450
    1,066
    Yes measure first before connecting your stereo.

    The top terminals are the 15V secondary with a tap at 13V. You are using only the primary side as an autotransformer.
     
  15. sunnyswh

    Thread Starter New Member

    Dec 19, 2014
    12
    0
    Thanks Mike! I will collect parts and make it according to your advices. Another question, I was looking for off-the-shelf transformer before I found this old part from the light source. I found they are generally sold as 250W, 500W or higher. My question is, if we use the 250W one, the output voltage is 110V, then the current is 2.27A. If we use this for the 60W stereo, which requires 110V and the current is 0.55A. The current supplied is much higher than the current required. Would it burn the stereo? It must be a very silly question to you , but it is a mystery to me. Sorry I forgot all I have been taught in school.
     
  16. MrChips

    Moderator

    Oct 2, 2009
    12,452
    3,371
    No. The current and power drawn is determined by the load. If the appliance draws 60W then that is what it will take out of the transformer even if the transformer is rated at 250W.

    A power rating of 250W means that you should not attempt to draw more than 250W.
    What would be the consequences? The voltage supplied will fall. The transformer will get hot and would become a fire hazard.
     
  17. sunnyswh

    Thread Starter New Member

    Dec 19, 2014
    12
    0
    thanks! Interesting! I am keen to go back to text book now. I assume the transformer gets hot, the consequence of overdraw, is due to increased current? Why the voltage falls and current increases rather than current falls and voltage increases?
     
  18. MrChips

    Moderator

    Oct 2, 2009
    12,452
    3,371
    Two things are at play.

    Firstly, all transformers have internal DC resistance depending on the length and size of the windings. The gauge of the winding is optimized for the desired maximum carrying current. The more current you draw, the more heat is dissipated in the winding.

    Secondly, the core of the transformer is also optimized for the desired maximum power output. When you attempt to draw more power than what the transformer is designed to supply, the core will reach magnetic saturation. As you attempt to draw more current the output voltage will fall since the power output cannot go any higher.

    The bottom line is, a transformer rated at higher power will need fatter wires and a larger core and hence would cost more. Hence you should purchase and install a properly sized transformer to suit the power requirements. Going 20% higher that your maximum requirements will provide some headroom and keep things cool.

    Edit:

    I should add that transformers with the same specifications from different manufacturers do not perform in the same manner. Many transformers perform poorly at their rated output. Transformers manufactured by Hammond perform well right up to their rated output.
     
    Last edited: Dec 22, 2014
  19. sunnyswh

    Thread Starter New Member

    Dec 19, 2014
    12
    0

    Hi Mike, it is done. the output is now 119.5V. Thanks! one question: how much of variation in voltage can an equipment tolerate? How to calculate it?
     
  20. sunnyswh

    Thread Starter New Member

    Dec 19, 2014
    12
    0
    Thanks a lot for your advices!
     
Loading...